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Bird-Friendly
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The area o glass on a aade is the strongest predictor o threat to birds. The aade o SauerbruchHuttons Brandhorst Museum in Munich is a brilliant example o the creative use o non-glass materials.Photos: Tony Brady (let), Anton Schedlbauer (background)
(Front cover) Boris Penas Public Health Oce building in Mallorca, Spain, sports a galvanized, electro-used steelaade. Photo courtesy o Boris Pena
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3Bird-Friendly Building Design
Table of Contents
Executive Summary 5
Introduction 6
Why Birds Matter 7
The Legal Landscape 7
Glass: The Invisible Threat 7
Lighting: Exacerbating the Threat 7
Birds and the Built Environment 8
Impact o Collisions on Bird Populations 8
The Impact o Trends in Modern Architecture 8
Dening Whats Good For Birds 9
ABCs Bird-Friendly Building Standards 9
Problem: Glass 10Properties o Glass 11
Reections 11
Transparency 11
Black Hole or Passage Efect 11
Factors Afecting Rates o Bird Collisions 11
at a Particular Location
Building Design 12
Type o Glass 12
Building Size 12
Building Orientation and Siting 12Design Traps 12
Reected Vegetation 14
Green Roos and Walls 14
Local Conditions 14
Lighting 14
Solutions: Glass 16
Facades, netting, screens, grilles, 18
shutters, exterior shadesAwnings and Overhangs 20
UV Patterned Glass 20
Angled Glass 20
Patterns on Glass 22
Opaque and Translucent Glass 24
Shades, Blinds, and Curtains 26
Window Films 26
Temporary Solutions 26
Decals 26
Problem: Lighting 28
Beacon Efect and Urban Glow 29
Solutions: Lighting Design 30
Lights Out Programs 31
Solutions: Legislation 34
Appendix I: The Science of Bird Collisions 37
Magnitude o Collision Deaths 37
Patterns o Mortality 37
Avian Vision and Collisions 38
Avian Orientation and the Earths Magnetic Field 38
Birds and Light Pollution 39
Light Color and Avian Orientation 40
Weather Impact on Collisions 40
Landscaping and Vegetation 40
Research: Deterring Collisions 41
Appendix II: Bird Migration 44
Diurnal Migrants 45
Nocturnal Migrants 46
Local movements 47
Appendix III: Evaluating Collision Problems 48
A Building Owners Toolkit
Seasonal Timing 49
Diurnal Timing 49
Weather 49
Location 50
Local Bird Populations 50
Research 51
Appendix IV: Example Policy 52
References 54
Acknowledgments 57
Disclaimer 57
Ruby-throated Hummingbird: Greg Lavaty
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4 Bird-Friendly Building Design
41 Cooper Square in New York City, by Morphosis Architects, eatures a skin o perorated steel panelsronting a glass/aluminum window wall. The panels reduce heat gain in summer and add insulat ion
in winter while also making the building saer or birds. Photo: Christine Sheppard, ABC
Issues o cost prompted Hariri Pontarini Architects, in a joint venture with Robbie/
Young + Wright Architects, to revise a planned glass and limestone aade on theSchool o Pharmacy building at the University o Waterloo, Canada. The new designincorporates watercolors o medicinal plants as photo murals. Photo: Anne H. Cheung
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5Bird-Friendly Building Design
Collision with glass is the single biggest known killer o birds in the United States, claiming hundreds o millions or more lives
each year. Unlike some sources o mortality that predominantly kill weaker individuals, there is no distinction among victims
o glass. Because glass is equally dangerous or strong, healthy, breeding adults, it can have a particularly serious impact onpopulations.
Bird kills at buildings occur across the United States. We know more about mortality patterns in cities, because that is where
most monitoring takes place, but virtually any building with glass poses a threat wherever it is. The dead birds documented by
monitoring programs or turned in to museums are only a raction o the birds actually killed. The magnitude o this problem
can be discouraging, but there are solutions i people can be convinced to adopt them.
The push to make buildings greener has ironically increased bird mortality because it has promoted greater use o glass
or energy conservation, but green buildings dont have to kill birds. Constructing bird-riendly buildings and eliminating
the worst existing threats requires imaginative design and recognition that not only do birds have a right to exist, but their
continued existence is a value to humanity.
New construction can incorporate bird-riendly design strategies rom the beginning. However, there are many ways to
reduce mortality rom existing buildings, with more solutions being developed all the time. Because the science is constantly
evolving, and because we will always wish or more inormation than we have, the temptation is to postpone action in
the hope that a panacea is just round the corner, but we cant wait to act. We have the tools and the strategies to make a
dierence now. Architects, designers, city planners, and legislators are key to solving this problem. They not only have access
to the latest building construction materials and concepts, they are also thought leaders and trend setters in the way we build
our communities and prioritize building design issues.
This publication, produced by American Bird Conservancy (ABC), and built upon the pioneering work o the NYC AudubonSociety, aims to provide planners, architects, designers, bird advocates, local authorities, and the general public with a clear
understanding o the nature and magnitude o the threat glass poses to birds. This edition includes a review o the science
behind available solutions, examples o how those solutions can be applied to new construction and existing buildings, and
an explanation o what inormation is still needed. We hope it will spur individuals, businesses, communities, and governments
to address this issue and make their buildings sae or birds.
ABCs Collisions Program works at the national level to reduce bird mortality by coordinating with local organizations,
developing educational programs and tools, conducting research, developing centralized resources, and generating
awareness o the problem.
Executive Summary
A bird, probably a dove, hit the window o an Indianahome hard enough to leave this ghostly image on theglass. Photo: David Fancher
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Introduction
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7Bird-Friendly Building Design
Why Birds MatterFor many people birds and nature have intrin-
sic worth. Birds have been important to humans
throughout history, oten used to symbolize cultural
values such as peace, reedom, and delity.
In addition to the pleasure they can bring to people,we depend on them or critical ecological unctions.
Birds consume vast quantities o insects, and control
rodent populations, reducing damage to crops and
orests, and helping limit the transmission o diseas-
es such as West Nile virus, dengue ever, and malaria.
Birds play a vital role in regenerating habitats by pol-
linating plants and dispersing seeds.
Birds are also a vast economic resource. According
to the U.S. Fish and Wildlie Service, bird watching isone o the astest growing leisure activities in North
America, and a multi-billion-dollar industry.
The Legal LandscapeAt the start o the 20th Century, ollowing the
extinction o the Passenger Pigeon and the near
extinction o other bird species due to unregulated
hunting, laws were passed to protect bird popula-
tions. Among them was the Migratory Bird Treaty
Act (MBTA), which made it illegal to kill a migratorybird without a permit. The scope o this law, which
is still in eect today, extends beyond hunting, such
that anyone causing the death o a migratory bird,
even i unintentionally, can be prosecuted i that
death is deemed to have been oreseeable. This
may include bird deaths due to collisions with glass,
though there have yet to be any prosecutions in the
United States or such incidents. Violations o the
(Opposite) The White-throated Sparrow is the most requent victim ocollisions reported by urban monitoring programs. Photo: Robert Royse
The hummingbird habit o trap-lining fying quickly rom one eedingspot to another causes collisions when fowers or eeders are refected inglass. Photo: Terry Sohl
MBTA can result in nes o up to $500 per incident
and up to six months in prison.
The Bald and Golden Eagle Protection Act (originally
the Bald Eagle Protection Act o 1940), the Endan-
gered Species Act (1973), and the Wild Bird Conser-
vation Act (1992) provide urther protections orbirds that may be relevant to building collisions.
Recent legislation, primarily at the city and state
level, has addressed the problem o mortality rom
building collisions and light pollution. Cook County,
Illinois, San Francisco, Caliornia, Toronto, Canada,
and the State o Minnesota have all passed laws or
ordinances aimed at reducing bird kills, while other
authorities have pushed or voluntary measures.
The International Dark Skies Foundation, an environ-mental organization whose mission is to preserve
and protect the nighttime environment now ac-
tively supports legislation designed to protect birds
by curbing light emissions.
Glass: The Invisible ThreatGlass can be invisible to both birds and humans.
Humans learn to see glass through a combination
o experience (how many o us at some time in our
lives have walked into a glass door or seen some-body do so?), visual cues, and expectation, but birds
are unable to use these signals. Most birds rst en-
counter with glass is atal when they collide with it
at ull speed.
No one knows exactly how many birds are killed by
glass the problem exists on too great a scale, both
in terms o geography and quantity but estimates
range rom 100 million to one billion birds each year
in the United States. Despite the enormity o the
problem, however, currently available solutions can
reduce bird mortality while retaining the advantages
that glass oers as a construction material, without
sacricing architectural standards.
Lighting: Exacerbating the ThreatThe problem o bird collisions with glass is greatly
exacerbated by ar ticial light. Light escaping rom
building interiors or rom exterior xtures can attract
birds, particularly during migration on oggy nights
or when the cloud base is low. Strong beams o light
can cause birds to circle in conusion and collide
with structures, each other, or even the ground. Oth-
ers may simply land in lighted areas and must then
navigate an urban environment rie with other dan-
gers, including more glass.
Birds and the Built EnvironmentHumans rst began using glass in Egypt, around
3500 BCE. Glass blowing, invented by the Romans
in the early First Century CE, greatly increased the
ways glass could be used, including the rst use o
crude glass windows. Although the Crystal Palace in
London, England, erected in 1851, is considered by
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8 Bird-Friendly Building Design
architects to mark the beginning o the use o glass
as a structural element, the invention o foat glass in
the 1950s allowed mass production o modern win-
dows. In the 1980s development o new production
and construction technologies culminated in todays
glass skyscrapers.
Sprawling land-use patterns and intensied urban-
ization degrade the quality and quantity o bird
habitat across the globe. Cities and towns encroach
on riverbanks and shorelines. Suburbs, arms, and
recreation areas increasingly inringe upon wetlands
and woodlands. Some bird species simply abandon
disturbed habitat. For species that can tolerate dis-
turbance, glass is a constant threat, as these birds
are seldom ar rom human structures. Migrating
birds are oten orced to land in trees lining our side-walks, city parks, waterront business districts, and
other urban green patches that have replaced their
traditional stopover sites.
The amount o glass in a building is the strongest
predictor o how dangerous it is to birds. However,
even small areas o glass can be lethal. While bird kills
at homes are estimated at one to ten birds per home
The Common Yellowthroat may be the most common warblers in NorthAmerica and is also one o the most common victims o collisions with
glass. Photo: Owen Deutsch
in construction. This is maniest in an increase in
picture windows on private homes and new appli-
cations or glass are being developed all the time.
Unortunately, as the amount o glass increases, so
does the incidence o bird collisions.
In recent decades, growing concern or the en-vironment has stimulated the development o
green standards and rating systems. The best
known is the Green Building Councils (GBC) Leader-
ship in Energy and Environmental Design, or LEED.
GBC agrees that green buildings should not threaten
Wildlie, but until recently, did not include language
addressing the threat o glass to birds.
Their Resource Guide, starting with the 2009 edition,
calls attention to parts o existing LEED credits that
can be applied to reduce negative impacts on birds.
(One example: reducing light pollution saves energy
and benets birds.) As o October 14, 2011, GBC has
added Credit 55: Bird Collision Deterrence, to their
Pilot Credit Library (http://www.usgbc.org/ShowFile.
aspx?DocumentID=10402), drated by ABC, mem-
bers o the Bird-sae Glass Foundation, and the GBC
Site Subcommittee.
per year, the large number o homes multiplies that
loss to millions o birds per year in the United States.
Other actors can increase or decrease a buildings
impact, including the density and species composi-
tion o local bird populations, local geography, the
type, location, and extent o landscaping and nearby
habitat, prevailing wind and weather, and patterns omigration through the area. All must be considered
when planning bird-riendly buildings.
Impact o Collisions on Bird PopulationsAbout 25% o species are now on the U.S. WatchList
o birds o conservation concern (www.abcbirds.org/
abcprograms/science/watchlist/index.html), and
even many common species are in decline. Habitat
destruction or alteration on both breeding and win-
tering grounds remains the most serious man-madeproblem, but collisions with buildings are the largest
known atality threat. Nearly one third o the bird
species ound in the United States, over 258 species,
rom hummingbirds to alcons, are documented as
victims o collisions. Unlike natural hazards that pre-
dominantly kill weaker individuals, collisions kill all
categories o birds, including some o the strongest,
healthiest birds that would otherwise survive to
produce ospring. This is not sustainable and most
o the mortality is avoidable. This document is onepiece o a strategy to keep building collisions rom
increasing, and ultimately, to reduce them.
The Impact o Trends in ModernArchitectureIn recent decades, advances in glass technology
and production have made it possible to construct
buildings with all-glass curtain walls, and we have
seen a general increase in the amount o glass usedWarblers, such as this Black-and-white, are oten killed by window collisions
as they migrate. Photo: Luke Seitz
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Essential to this credit is quantiying the threat level
to birds posed by dierent materials and design
details. These threat actors are used to calculate an
index representing the buildings aade and that
index must be below a standard value to earn the
credit. The credit also requires adopting interior
and exterior lighting plans and post-constructionmonitoring. The section on Research in Appendix
I reviews the work underlying the assignment o
threat actors.
ABC is a registered provider o AIA continuing
education, with classes on bird-riendly design
and LEED Pilot Credit 55 available in ace-to-ace
and webinar ormats. Contac t Christine Sheppard,
[email protected], or more inormation.
Dening Whats Good or BirdsIt is increasingly common to see the phrase bird-
riendly used in a variety o situations to demonstrate
that a particular product, building, legislation, etc., is
not harmul to birds. All too oten, however, this term is
unaccompanied by a clear denition, and lacks a sound
scientic oundation to underpin its use.
Ultimately, dening bird riendly is a subjective task.
Is bird-riendliness a continuum, and i so, where does
riendly become unriendly? Is bird-riendly the same
as bird-sae? How does the denition change rom use
to use, situation to situation?
It is impossible to know exactly how many birds
a particular building will kill beore it is built, and
so realistically, we cannot declare a building to be
bird-riendly beore it has been careully monitored
or several years. However, there are several actors
that can help us predict whether a building will be
The Hotel Puerta America in Mexico City was designed by Jean Nouvel, andeatures external shades. This is a fexible strategy or sun control, as well aspreventing collisions; shades can be lowered selectively when and whereneeded. Photo: Ramon Duran
particularly harmul to birds or generally benign,
and we can accordingly dene simple bird-smart
standards that, i ollowed, will ensure a prospective
building poses a minimal potential hazard to birds.
ABCs Bird-Friendly Building Standard
A bird-riendly building is one where:
Atleast90%ofexposedfaadematerialfrom
ground level to 40 eet (the primary bird
collision zone) has been demonstrated in
controlled experiments1 to deter 70% or
more o bird collisions
Atleast60%ofexposedfaadematerialabove
the collisions zone meets the above standard
Therearenotransparentpassagewaysorcor-
ners, or atria or courtyards that can trap birds
Outsidelightingisappropriatelyshieldedand
directed to minimize attraction to night-
migrating songbirds2
Interiorlightingisturnedoatnightorde-
signed to minimize light escaping through
windows
Landscapingisdesignedtokeepbirdsaway
rom the buildings aade3
Actualbirdmortalityismonitoredandcompen-
sated or (e.g., in the orm o habitat preserved
or created elsewhere, mortality rom other
sources reduced, etc.)
1See the section Research: Deterring Bird Collisions inAppendix I or inormation on these controlledstudies.
2See the section Solutions: Lighting Design on page 31
3See Landscaping and Vegetation, Appendix I on Page 40
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Problem: Glass
The glass in this Washington, DC atrium poses a double hazard, drawingbirds to plants inside, as well as refecting sky above. Photo: ABC
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11Bird-Friendly Building Design
The Properties o GlassGlass can appear very dierently depending on a number o
actors, including how it is abricated, the angle at which it
is viewed, and the dierence between exterior and interior
light levels. Combinations o these actors can cause glass to
look like a mirror or dark passageway, or to be completely
invisible. Humans do not actually see most glass, but arecued by context such as mullions, roos or doors. Birds, how-
ever, do not perceive right angles and other architectural
signals as indicators o obstacles or articial environments.
ReectionViewed rom outside, transparent glass on buildings is oten
highly refective. Almost every type o architectural glass,
under the right conditions, refects the sky, clouds, or nearby
habitat amiliar and attractive to birds. When birds try to fy
to the refected habitat, they hit the glass. Refected vegeta-
tion is the most dangerous, but birds also attempt to fy pastrefected buildings or through refected passageways.
TransparencyBirds strike transparent windows as they attempt to access
potential perches, plants, ood or water sources, and other
lures seen through the glass. Glass skywalks joining build-
ings, glass walls around planted atria, windows installed per-
pendicularly on building corners, and exterior glass handrails
or walkway dividers are dangerous because birds perceive
an unobstructed route to the other side.
Black Hole or Passage EfectBirds oten fy through small gaps, such as spaces between
leaves or branches, nest cavities, or other small openings. In
some light, glass can appear black, creating the appearance o
just such a cavity or passage through which birds try to fy.
Factors Afecting Rates o Bird Collisionsor a Particular Building
Every site and every building can be characterized as aunique combination o risk actors or collisions. Some,
particularly aspects o a buildings design, are very building-
specic. Many negative design eatures can be readily coun-
tered, or, in new construction, avoided. Others, or example
a buildings location and siting, relate to migration routes,
regional ecology, and geographyactors that are dicult i
not impossible to modiy.
The glass-walled towers o the Time-Warner Center in New York City appear to birdsas just another piece o the sky. Photo: Christine Sheppard, ABC
Architectural cues show people that only one panel on the aceo this shelter is open; to birds, all the panels appear to be open.Photo: Christine Sheppard, ABC
Transparent handrails are a dangerous trend or birds, especiallywhen they ront vegetation. Photo: Christine Sheppard, ABC
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12 Bird-Friendly Building Design
Building DesignGlass causes virtually all bird collisions with buildings. The
relative threat posed by a particular building depends sub-
stantially on the amount o exposed glass, as well as the
type o glass used, and the presence o glass design traps.
Klem (2009) in a study based on data rom Manhattan, New
York, ound that a 10% increase in the area o refective andtransparent glass on a building aade correlated with a 19%
increase in the number o atal collisions in spring and a 32%
increase in all.
Type o GlassThe type o glass used in a building is a signicant compo-
nent o its danger to birds. Mirrored glass is oten used to
make a building blend into an area by refecting its sur-
roundings. Unortunately, this makes those buildings espe-
cially deadly to birds. Mirrored glass is refective at all timeso day, and birds mistake refections o sky, trees, and other
habitat eatures or reality. Non-mirrored glass can be highly
refective at one time, and at others, appear transparent or
dark, depending on time o day, weather, angle o view, and
other variables, as with the window pictured below. Tinted
glass reduces collisions, but only slightly. Low-refection
glass may be less hazardous in some situations, but does not
actively deter birds and can create a passage eect, appear-
ing as a dark void that could be fown through (see page 11).
Building SizeAs building size increases or a particular design, so usually
does the amount o glass, making larger buildings more o a
threat. It is generally accepted that the lower stories o build-
ings are the most dangerous because they are at the same
level as trees and other landscape eatures that attract birds.
However, monitoring programs accessing setbacks and roos
o tall buildings are nding that birds also collide with higher
levels.
Building Orientation and SitingBuilding orientation in relation to compass direction has not
been implicated as a actor in collisions, but siting o a build-
ing with respect to surrounding habitat and landscaping can
be an issue, especially i glass is positioned so that it refects
vegetation. Physical eatures such as outcrops or pathways
that provide an open fight path through the landscape canchannel birds towards or away rom glass and should be
considered early in the design phase.
Design TrapsWindowed courtyards and open-topped atria can be death
traps or birds, especially i they are heavily planted. Birds
fy down into such places, and then try to leave by fying
directly towards refections on the walls. Glass skywalks and
outdoor handrails, and building corners where glass walls or
windows are perpendicular are dangerous because birds cansee through them to sky or habitat on the other side.
Birds fying rom a meadow on the l et are channeled towards the glass doors o thisbuilding by a rocky outcrop to the right o the path. Photo: Christine Sheppard, ABC
Large acing panes o glass can appear to be a clear pathway.Photo: Christine Sheppard, ABC
The same glass can appear transparent or highly refective,depending on weather or time o day. Photo: Christine
Sheppard, ABC
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Mirrored glass is dangerous at all times o day, whether it refects vegetation, sky, or simply open spacethrough which a bird might try to fy. Photo: Christine Sheppard, ABC
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14 Bird-Friendly Building Design
Reected VegetationGlass that refects shrubs and trees causes more collisions
than glass that refects pavement or grass (Gelb and Delec-
retaz,2006).Studieshaveonlyquantiedvegetationwithin
15-50 eet o a aade, but refections can be visible at much
greater distances. Vegetation around buildings will bring
more birds into the vicinity o the building; the refection o
that vegetation brings more birds into the glass. Taller trees
and shrubs correlate with more collisions. It should be kept
in mind that vegetation on slopes near a building will refectin windows above ground level. Studies with bird eeders
(Klem et al., 1991) have shown that atal collisions result
when birds fy towards glass rom more than a ew eet away.
Green Roos and WallsGreen roos bring habitat elements attractive to birds to
higher levels, oten near glass. However, recent work shows
that well designed green roos can become unctional
ecosystems, providing ood and nest sites or birds. Siting
o green roos, as well as green walls and rootop gardens
should thereore be careully considered, and glass adjacent
to these eatures should have protection or birds.
Local ConditionsAreas where og is common may exacerbate local light pol-
lution (see below). Areas located along migratory pathwaysor where birds gather prior to migrating across large bodies
o water, or example, in Toronto, Chicago, or the southern
tip o Florida, expose birds to highly urban environments
and have caused large mortality events (see Appendix II or
additional inormation on how migration can infuence bird
collisions).
LightingInterior and exterior building and landscape lighting can
make a signicant dierence to collisions rates in any one lo-cation. This phenomenon is dealt with in detail in the section
on lighting.
Refections on home windows are a signicant source o bird mortality. The partiallyopened vertical blinds seen here may break up the refection enough to reduce thehazard to birds. Photo: Christine Sheppard, ABC
Plantings on setbacks and rootops can attract birds to glassthey might otherwise avoid. Photo: Christine Sheppard, ABC
Vines cover most o these windows, but birds might fy intothe dark spaces on the right. Photo: Christine Sheppard, ABC
Planted, open atrium spaces lure birds down, then prove dangerous when birds try tofy out to refections on surrounding windows. Photo: Christine Sheppard, ABC
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This atrium has more plants than anywhere outside on the surrounding streets, making the glass deadly or birds seeking ood in this area.Photo: Christine Sheppard, ABC
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Solutions: Glass
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It is possible to design buildings that can reasonably be
expected not to kill birds. Numerous examples exist, not
necessarily designed with birds in mind, but to be unctional
and attractive. These buildings may have windows, but use
screens, latticework, grilles, and other devices outside the
glass or integrated into the glass.
Finding glass treatments that can eliminate or greatly reduce
bird mortality while minimally obscuring the glass itsel
has been the goal o several researchers, including Martin
Rssler, Dan Klem, and Christine Sheppard. Their research,
discussed in more detail in Appendix I, has ocused primar-
ily on the spacing, width, and orientation o lines marked on
glass, and has shown that patterns covering as little as 5% o
the total glass surace can deter 90% o strikes under experi-
mental conditions. They have consistently shown that most
birds will not attempt to fy through horizontal spaces lessthan 2 high nor through vertical spaces 4 wide or less. We
reer to this as the 2 x 4 rule. There are many ways that this
can be used to make buildings sae or birds.
Designing a new structure to be bird riendly does not need
to restrict the imagination or add to the cost o construc-
tion. Architects around the globe have created ascinating
and important structures that incorporate little or no ex-
posed glass. In some cases, inspiration has been born out o
unctional needs, such as shading in hot climates, in others,
aesthetics; being bird-riendly was usually incidental. Ret-
rotting existing buildings can oten be done by targeting
problem areas, rather than entire buildings.
Emilio Embasz used creative lighting strategies to illuminate his Casa de Respira Espiritual, located north o Seville, Spain. Much o thestructure and glass are below grade, but are lled with refected light. Photo courtesy o Emilio Ambasz and Associates
(Opposite) The external glass screen on the GSA Regional Field Oce in Houston, TX,designed by Page Southerland Page, means windows are not v isible rom many angles.Photo: Timothy Hursley
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18 Bird-Friendly Building Design
Facades, netting, screens, grilles, shutters,exterior shadesThere are many ways to combine the benets o glass with
bird-sae or bird-riendly design by incorporating elements
that preclude collisions without completely obscuring vi-
sion. Some architects have designed decorative acades that
wrap entire structures. Recessed windows can unctionallyreduce the amount o visible glass and thus the threat to
birds. Netting, screens, grilles, shutters and exterior shades
are more commonly used elements that can make glass
sae or birds. They can be used in retrots or be an integral
part o an original design, and can signicantly reduce bird
mortality.
Beore the current age o windows that are unable to be
opened, screens protected birds in addition to their primary
purpose o keeping bugs out. Screens and nets are still
among the most cost-eective methods or protecting birds,
and netting can oten be installed so as to be nearly invisible.
Netting must be installed several inches in ront o the win-
dow, so impact does not carry birds into the glass. Severalcompanies sell screens that can be attached with suction
cups or eye hooks or small areas o glass. Others specialize
in much larger installations.
Decorative grilles are also part o many architectural tradi-
tions, as are shutters and exterior shades, which have the
additional advantage that they can be closed temporarily,
specically during times most dangerous to birds, such as
migration and fedging (see Appendix II).
Functional elements such as balconies and balustrades can
act like a aade, protecting birds while providing an amenity
or residents.
FOA made extensive use o bamboo in the design o thisMadrid, Spain public housing block. Shutters are an excellentstrategy or managing bird collisions as they can be closed asneeded. Photo courtesy o FOA
The aade o the New York Times building, by FX Fowle and Renzo Piano, is composed o ceramic rods, spaced to let occupants see out, while minimizing
the extent o exposed glass. Photo: Christine Sheppard, ABC
External shades on Renzo Pianos Caliornia Academy o Sciences in San Francisco arelowered during migration seasons to eliminate collisions. Photo: Mo Flannery
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The combination o shades and balustrades screens glass on Os ArchitectsApartments on the Coast in Izola, Slovenia. Photo courtesty o Os
Instead o glass, this side o Jean Nouvels Institute Arabe du Monde in Paris,France eatures motor-controlled apertures that produce ltered light in theinterior o the building. Photo: Vicki Paull
For the Langley Academy in Berkshire, UK, Foster + Par tnersused louvers to control light and ventilation, also making thebuilding sae or birds. Photo: Chris Phippen Os
A series o balconies, such as those pictured here, can hide glass rom view.Photo: Elena Cazzaniga
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20 Bird-Friendly Building Design
Awnings and OverhangsOverhangs have been said to reduce collisions, however,
they do not eliminate refections, and only block glass rom
the view o birds fying above. They are thus o limited eec-
tiveness as a general strategy.
UV Patterned GlassBirds can see into the ultraviolet (UV) spectrum o light, a
rangelargelyinvisibletohumans(seepage36).UV-reec-
tive and/or absorbing patterns (transparent to humans but
visible to birds) are requently suggested as the optimal
solution or many bird collision problems. Progress in the
search or bird-riendly UV glass has been slow, however,
due to the inherent technical complexities, and because,
in the absence o widespread legislation mandating bird-
riendly glass, only a ew glass companies recognize this as
a market opportunity. Research indicates that UV patternsneed strong contrast to be eective.
Angled GlassIn a study (Klem et al., 2004) comparing bird collisions with
vertical panes o glass to those tilted 20 degrees or 40 de-
grees, the angled glass resulted in less mortality. For this
reason, it has been suggested that angled glass should be
incorporated into buildings as a bird-riendly eature. While
angled glass may be useul in special circumstances, the
birds in the study were fying parallel to the ground romnearby eeders. In most situations, however, birds approach
glass rom many angles, and can see glass rom many per-
spectives. Angled glass is not recommended as appropriate
or useul strategy. The New York Times printing plant, pic-
tured opposite, clearly illustrates this point. The angled glass
curtain wall shows clear refections o nearby vegetation,
visible rom a long distance away.
Overhangs block viewing o glass rom some angles, but do notnecessarily eliminate refections. Photo: Christine Sheppard, ABC
Deeply recessed windows, such as these on Stephen Holls Simmons Hall at MIT, canblock viewing o glass rom most angles. Photo: Dan Hill
Refections in this angled aade can be seen clearly over a longdistance, and birds can approach the glass rom any angle. Photo:Christine Sheppard, ABC
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Translucent glass panels on the Kunsthaus Bregenz in Austria, designed by Atelier Peter Zumthor, providelight and air to the building interior, without dangerous refections. Photo: William Heltz
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22 Bird-Friendly Building Design
Patterns on GlassPatterns are oten applied to glass to reduce the trans-
mission o light and heat; they can also provide some
design detail. When designed according to the 2x4
rule, (see p. 17) patterns on glass can also prevent bird
strikes. External patterns on glass deter collisions e-
ectively because they block glass refections, acting likea screen. Ceramic dots or rits and other materials can
be screened, printed, or otherwise applied to the glass
surace. This design element, useul primarily or new
construction, is currently more common in Europe and
Asia, but is being oered by an increasing number o
manuacturers in the United States.
More commonly, patterns are applied to an internal
surace o double-paned windows. Such designs may
not be visible i the amount o light refected rom therit is insucient to overcome refections on the glass
outside surace. Some internal rits may only help break
up refections when viewed rom some angles and in
certain light conditions. This is particularly true or large
windows, but also depends on the density o the rit pat-
tern. The internet company IACs headquarters building
in New York City, designed by Frank Gehry, is composed
entirely o ritted glass, most o high density. No collision
mortalities have been reported at this building ater two
years o monitoring by Project Sae Flight. Current re-search is testing the relative eectiveness o dierent rit
densities, congurations, and colors.
The glass acade o SUVA Haus in Basel, Switzerland, reno-vated by Herzog and de Meuron, is screen-printed on theoutside with the name o the company owning the building.Photo: Miguel Marqus Ferrer
Dense stripes o internal rit on University HospitalsTwinsburg Health Center in Cleveland, by Westlake, Reed,Leskosky will overcome virtually all refections. Photo:Christine Sheppard, ABC
The Studio Gangs Aqua Tower in Chicago was designed with birds in mind.
Strategies include ritted glass and balcony balustrades. Photo: Tim Bloomquist
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23Bird-Friendly Building Design
The dramatic City Hall o Alphen aan den Rijn in the Netherlands, designedby Erick van Egeraat Associated Architects, eatures a aade o etched glass.Photo: Dik Naagtegal
A detail o a pattern printed on glass at the Cottbus Media Centre inGermany. Photo: Evan Chakro
RAUs World Wildlie Fund Headquarters in the Netherlands useswooden louvers as sunshades; they also diminish the area o glassvisible to birds. Photo courtesy o RAU
External rit, as seen here on the Lile Museum o Fine Arts, by Ibosand Vitart, is more eective at breaking up refections than patternson the inside o the glass. Photo: G. Fessy
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24 Bird-Friendly Building Design
Opaque and Translucent GlassOpaque, etched, stained, rosted glass, and glass block
can are excellent options to reduce or eliminate collisions,
and many attractive architectural applications exist. They
can be used in retrots but are more commonly in new
construction.
Frosted glass is created by acid etching or sandblasting
transparent glass. Frosted areas are translucent, but dierent
nishes are available with dierent levels o light transmis-
sion. An entire surace can be rosted, or rosted patterns
can be applied. Patterns should conorm to the 2x4 rule de-
scribed on page 17. For retrots, glass can also be rosted by
sandblasting on site.
Stained glass is typically seen in relatively small areas but can
be extremely attractive and is not conducive to collisions.
Glass block is extremely versatile, can be used as a design
detail or primary construction material, and is also unlikely
to cause collisions.
While some internal ritted glass patterns can be over-
come by refections, Frank Gehrys IAC Headquarters inManhattan is so dense that the glass appears opaque.Photo: Christine Sheppard, ABC
Renzo Pianos Hermes Building in Tokyo has a aade o glass block.Photo: Mariano Colantoni
Frosted glass aade on the Wexord Science and Technology building in Philadelphia,by Zimmer, Gunsul, Frasca. Photo: Walker Glass
UN Studios Het Valkho Museum in Nijmegan, TheNetherlands, uses translucent glass to diuse light tothe interior, which also reduces dangerous refections.Photo courtesy o UN Studio.
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25Bird-Friendly Building Design
A dramatic use o glass block denotes the Hecht Warehouse in Washington, DC,by Abbott and Merkt. Photo: Sandra Cohen-Rose and Colin Rose
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26 Bird-Friendly Building Design
Internal Shades, Blinds, and CurtainsLight colored shades are oten recommended as a way to de-
ter collisions. However, they do not eectively reduce refec-
tions and are not visible rom acute angles. Blinds have the
same problems, but when visible and partly open, they are
more likely to break up refections than solid shades.
Window FilmsCurrently, most patterned window lms are intended or use
inside structures as design elements or or privacy, but this is
beginning to change. 3MTM ScotchcalTM Perorated Window
Graphic Film, also known as CollidEscape, is a well-known
external solution. It covers the entire surace o a window,
appears opaque rom the outside, but still permits a view out
rom inside. Interior lms, when applied correctly, have held
up well in external applications, but this solution has not yet
been tested over decades. A lm with a pattern o narrow,horizontal stripes was applied to a building, in Markham, On-
tario and successully eliminated collisions. Another lm has
been eective at the Philadelphia Zoos Bear Country exhibit
(see photo on opposite page). In both cases, the response o
people has also been positive.
Temporary SolutionsIn some circumstances, especially or homes and small build-
ings, quick, low-cost, temporary solutions such as making
patterns on glass with tape or paint can be very eective.
Even a modest eort can reduce collisions. Such measures
can be applied when needed and are most eective ollow-
ing the 2x4 rule. For more inormation, see ABCs inorma-tive fyer You Can Save Birds rom Flying into Windows at
www.abcbirds.org/abc
DecalsDecals are probably the most popularized solution to bird
collisions, but their eectiveness is widely misunderstood.
Birds do not recognize decals as silhouettes o birds, spider
webs, or other items, but simply as obstacles that they may
try to fy around. Decals are most eective i applied ollow-ing the 2 x 4 rule, but even a ew may reduce collisions.
Because decals must also be replaced requently, they are
usually considered a short-term strategy or small windows.
A single decal is ineective or collision prevention on a window o this size, as birdswill simply attempt to fy around it. Photo: Christine Sheppard, ABC
Tape decals (Window Alert shown here) placed ollowing the 2 x 4 rule can be eectiveat deterring collisions. Photo: Christine Sheppard, ABC
ABC BirdTape
Photos : Dariusz Zdziebkowski, ABC
ABC, with support rom the
Rusinow Family Foundation, has
produced ABC BirdTape to make
home windows saer or birds.This easy-to-apply tape lets birds
see glass while letting you see
out, is easily applied, and lasts
up to our years.
For more inormation, visit
www.ABCBirdTape.org
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This window at the Philadelphia Zoos Bear Country exhibit was the site o requent birdcollisions until this window lm was applied. Collisions have been eliminated, with nocomplaints rom the public. Photo courtesy o Philadelphia Zoo
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Problem: Lighting
Each white speck seen here is a bird, trapped in the beams olight orming the 9/11 Tribute in Lightin New York City. Volunteerswatch during the night and the lights are turned o briefy i largenumbers o birds are observed. Photo: Jason Napolitano
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29Bird-Friendly Building Design
Articial light is increasingly recognized as a negative actor
forhumansaswellaswildlife.RichandLongcore(2006)have
gathered comprehensive reviews o the impact o ecological
light pollution on vertebrates, insects, and even plants. For
birds especially, light can be a signicant and deadly hazard.
Beacon Efect and Urban GlowLight at night, especially during bad weather, creates con-
ditions that are particularly hazardous or night-migrating
birds. Typically fying at altitudes over 500 eet, migrants
oten descend to lower altitudes during inclement weather,
where they may encounter articial light rom buildings.
Water vapor in very humid air, og, or mist reracts light,
orming an illuminated halo around light sources.
There is clear evidence that birds are attracted to light, and
once close to the source, are unable to break away (Rich and
Longcore,2006;Pootetal.,2008;GauthreauxandBelser,
2006).Howdoesthisbecomeahazardtobirds?Whenbirds
encounter beams o light, especially in inclement weather,
they tend to circle in the illuminated zone, appearing dis-
oriented and unwilling or unable to leave. This has been
documented recently at the 9/11 Memorial in Lights, where
lights must be turned o briefy when large numbers o birds
become caught in the beams. Signicant mortality o migrat-
ing birds has been reported at oil platorms in the North Sea
and the Gul o Mexico. Van de Laar (2007) tested the impacton birds o lighting on an o-shore platorm. When lights
were switched on, birds were immediately attracted to the
platorm in signicant numbers. Birds dispersed when lights
were switched o. Once trapped, birds may collide with
structures or each other, or all to the ground rom exhaus-
tion, where they are at risk rom predators.
While mass mortalities at very tall illuminated structures
(such as skyscrapers) during inclement weather have
received the most attention, mortality has also been
associated with ground-level lighting during clear weather.
Light color also plays a role, with blue and green light much
saer than white or red light. Once birds land in lighted areas,
they are at risk rom colliding with nearby structures as they
orage or ood by day.
In addition to killing birds, overly-lit buildings waste electric-
ity, and increase greenhouse gas emissions and air pollu-
tion levels. Poorly designed or improperly installed outdoor
xtures add over one billion dollars to electrical costs in the
United States every year, according to the I nternational Dark
Skies Association. Recent studies estimate that over two
thirds o the worlds population can no longer see the Milky
Way, just one o the nighttime wonders that connect people
with nature. Together, the ecological, nancial, and cultural
impacts o excessive building lighting are compelling rea-
sons to reduce and rene light usage.
Houston skyline at night. Photo: Je Woodman
Overly-lit buildings waste electricity and increase greenhousegas emissions and air pollution levels, as well as posing a threatto birds. Photo: Matthew Haines
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Solutions: Lighting Design
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31Bird-Friendly Building Design
Reducing exterior building and site lighting has proven e-
ective at reducing mortality o night migrants. At the same
time, these measures reduce building energy costs and de -
crease air and light pollution. Ecient design o lighting sys-
tems plus operational strategies to reduce light trespass or
spill light rom buildings while maximizing useul light are
both important strategies. In addition, an increasing body oevidence shows that red lights and white light (which con-
tains red wavelengths) particularly attract and conuse birds,
while green and blue light have ar less impact.
Light pollution is largely a result o inecient exterior light-
ing, and improving lighting design usually produces savings
greater than the cost o changes. For example, globe xtures
permit little control o light, which shines in all directions, re-
sulting in a loss o as much as 50% o energy, as well as poor
illumination. Cut-o shields can reduce lighting loss and per-
mit use o lower powered bulbs.
Most vanity lighting is unnecessary. However, when it is
used, building eatures should be highlighted using down-
lighting rather than up-lighting. Where light is needed or
saety and security, reducing the amount o light trespass
outside o the needed areas can help by eliminating shad-
ows. Spotlights and searchlights should not be used during
bird migration. Communities that have implemented pro-
grams to reduce light pollution have not ound an increase
in crime.
Using automatic controls, including timers, photo-sensors,
and inrared and motion detectors is ar more eective than
reliance on employees turning o lights. These devices gen-
erally pay or themselves in energy savings in less than a
year. Workspace lighting should be installed where needed,
rather than lighting large areas. In areas where indoor lights
will be on at night, minimize perimeter lighting and/or draw
shades ater dark. Switching to
daytime cleaning is a simple
way to reduce lighting while
also reducing costs.
Lights Out ProgramsBirds evolved complex, comple-
mentary systems or orientation
and vision long beore humans
developed articial light. We
still have much more to learn,
especially the dierences be-
tween species, but recent sci-
ence has begun to clariy how
articial light poses a threat to birds, especially nocturnal mi-
grants. These birds use a magnetic sense which is dependent
on dim light rom the blue-green end o the spectrum.
Research has shown that dierent wavelengths cause di-
erent behaviors, with yellow and red light preventing ori-
entation. Dierent intensities o light also produce dierent
(Opposite) Fixtures such as these reduce light pollution, saving energy and money, andreducing negative impacts on birds. Photo: Dari usz Zdziebkowski, ABC
Shielded light xtures are widely available inmany dierent styles. Photo: Susan Harder
Reprinted courtesy o DarkSkySociety.org
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32 Bird-Friendly Building Design
reactions. Despite the complexity o this issue, there is one
simple way to reduce mortality: turn lights o.
Across the United States and Canada, Lights Out programs
at the municipal and state level encourage building owners
and occupants to turn out lights visible rom outside during
spring and all migration. The rst o these, Lights Out Chi-
cago, was started in 1995, ollowed by Toronto in 1997. There
are over twenty programs as o mid-2011.
The programs themselves are diverse. Some are directed by
environmental groups, others by government departments,
and still others by partnerships o organizations. Participa-
tion in some, such as Houstons, is voluntary. Minnesota
mandates turning o lights in state-owned and -leased
buildings, while Michigans governor proclaims Lights Out
dates annually. Many jurisdictions have a monitoring compo-
nent or work with local rehabilitators. Monitoring programs
can provide important inormation in addition to quantiy-
ing collision levels and documenting solutions. Toronto, or
example, determined that i short buildings emit more light,
they can be more dangerous to birds than tall building emit-ting less light.
Ideally, Lights Out programs would be in eect year round,
saving birds and energy costs and reducing emissions o
greenhouse gases. ABC stands ready to help develop new
programs and to support and expand existing programs.
Red: state ordinance
Yellow: cities in state-wideprograms
Turquoise: programin development
Blue: local programs
Lights Outmap legend
Distribution o Lights Out Programs in North America
Shielded lights, such as those shown above, cut down on lightpollution and are much saer or birds. Photo: Susan Harder
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33Bird-Friendly Building Design
Downtown Houston during Lights Out. Photo: Je Woodman
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34 Bird-Friendly Building Design
Solutions: Legislation
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35Bird-Friendly Building Design
Changing human behavior is generally a slow pro-
cess, even when the change is uncontroversial.
Legislation can be a powerul tool or modiying be-
havior. Conservation legislation has created reserves,
reduced pollution, and protected threatened spe-
cies and ecosystems. Initial eorts to document bird
mortality and recommend ways to remediate col-lisions have more recently given way to legislation
that promotes bird-riendly design and reduction o
light pollution.
Most o these ordinances reer to external guide -
lines, rather than speciying how their goals must be
achieved, and because there are many guidelines,
created at dierent times and oten specic to par-
ticular places, this can lead to contradiction, conu-
sion, and cases o shopping or the cheapest option.
These ABC guidelines are intended to address colli-sions at a national level and may be distributed by
other groups.
One challenge in creating legislation is to provide
specic strategies and create objective measures
that architects can use to accomplish their task. ABC
has incorporated objective criteria into this docu-
ment and created a model ordinance to be ound in
Appendix V .
ABC is willing to partner with local groups in creat-ing additions to the Guidelines with local ocus and
to assist in promoting local, bird-riendly legislation.
Cook County, Illinois, was the rst to pass bird-
riendly construction legislation, sponsored by
then-Assemblyman Mike Quigley.
In2006,Toronto,Canada,proposedaGreenDe-
velopment Standard, initially a set o voluntary
guidelines to promote sustainable site and build-
ing design, including guidelines or bird-riendly
construction. Development Guidelines became
mandatory on January 1, 2011, but the process o
translating guidelines into blueprints is still under-way. San Francisco adopted Standards or Bird-sae
Buildings in September, 2011. Listed below are some
examples o current and pending ordinances at lev-
els rom ederal to municipal.
Federal (proposed)
Illinois Congressman Mike Quigley (D-IL) introduced theFederalBird-SafeBuildingsActof2011(HR1643),which
calls or each public building constructed, acquired, oraltered by the General Services Administration (GSA) to in-corporate, to the maximum extent possible, bird-sae build-
ing materials and design eatures. The legislation wouldrequire GSA to take similar actions on existing buildings,where practicable. Importantly, the bill has been deemedcost-neutral by the Congressional Budget Oce. See http://thomas.loc.gov/cgi-bin/query/z?c112:H.R.1643.IH
State: Minnesota (enacted)
Chapter 101, Article 2, Section 54: Between March 15 andMay 31, and between August 15 and October 31 eachyear, occupants o state-owned or state-leased build-ings must attempt to reduce dangers posed to migratingbirds by turning o building lights between midnight and
dawn, to the extent turning o lights is compatible withthe normal use o the buildings. The commissioner o ad-ministration may adopt policies to implement this require-ment. See www.revisor.leg.state.mn.us/laws/?id=101&doctype=Chapter&year=2009&type=0
State: Minnesota (enacted; regulationspending)
Beginning on July 1, 2010, all Minnesota State bondedprojects new and substantially renovated that have notalready started the schematic design phase on August 1,2009 will be required to meet the Minnesota SustainableBuilding 2030 (SB 2030) energy standards. Seewww.mn2030.umn.edu/
State: New York (pending)
BillS04204/A6342-A,theBird-friendlyBuildingsAct,re-quires the use o bird-riendly building materials and de-sign eatures in buildings. See http://assembly.state.ny.us/leg/?bn=S04204&term=2011
City: San Francisco (enacted)
The citys Planning Department has developed the rst seto objective standards in the nation, dening areas wherethe regulations are mandated and others where they arerecommended, plus including criteria or ensuring that
designs will be eective or protecting birds. See http://www.sf-planning.org/index.aspx?page=2506
City: Toronto
On October 27, 2009, the Toronto City Council passed amotion making parts o the Toronto Green Standard man-datory. The standard, which had previously been voluntary,applies to all new construction in the city, and incorporatesspecic Bird-Friendly Development Guidelines, designed toeliminate bird collisions with buildings both at night and inthe daytime.
Beginning January 31, 2010, all new, proposed low-rise,
non-residential, and mid- to high-rise residential and in-dustrial, commercial, and institutional development willbe required under Tier 1 o the Standard, which appliesto all residential apar tment buildings and non-residentialbuildings that are our stories tall or higher. See www.toronto.ca/planning/environment/greendevelopment.htm
United States Capitol, Washington, DC . Photo: stock.xchng
Song Sparrow: Greg Lavaty
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36 Bird-Friendly Building Design
The number of birds killed by collisions with glass every year is astronomical.
Hundreds o species o birds are kil led by collisions. These birds were collected by monitors with FLAP in Toronto, Canada. Photo: Kenneth Herdy
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37Bird-Friendly Building Design
Magnitude o Collision DeathsThe number o birds killed by collisions with glass ev-
ery year is astronomical. Based on studies o homesand commercial structures, Klem (1990) estimated
conservatively that each building in the United States
killsonetotenbirdsperyear.Using1986United
States Census data, he combined numbers o homes,
schools, and commercial buildings or a maximum
totalof97,563,626buildings.Dunn(1993)surveyed
5,500 people who ed birds at their homes and re-
corded window collisions. She derived an estimate
of0.65-7.7birddeathsperhomeperyearforNorth
America, supporting Klems calculation.
The number o buildings in the United States has
increasedsignicantlysince1986,andithasbeen
shown that commercial buildings generally kill more
than ten birds per year, as would be expected since
they have large expanses o glass (Hager et al., 2008;
OConnell, 2001). Thus, one billion annual atalities
is likely to be closer to reality, and possibly even too
low.
Klem et al., (2009a) used data rom New York CityAudubons monitoring o seventy-three Manhattan
building acades to estimate 0.5 collision deaths per
acre per year in urban environments, or a total o
about 34 million migratory birds annually colliding
with city buildings in the United States.
Patterns o MortalityIt is dicult to get a complete and accurate picture
o avian mortality rom collisions with glass. Collisiondeaths can occur at any time. Even intensive monitor-
ing programs only cover a portion o a city, usually
visiting the ground level o a given site at most once
a day and oten only during migration seasons. Many
city buildings have stepped roo setbacks that are
inaccessible to monitoring teams. Recognizing these
limitations, some papers have ocused on reports
rom homeowners on backyard birds (Klem, 1989;
Dunn, 1993) or on mortality o migrants in an urban
environment (Gelb and Delacretaz, 2009; Klem et al.,2009a, Newton, 1999). Others have analyzed collision
victims rom single, large-magnitude incidents (Sealy,
1985) or that have become part o museum collec-
tions(Snyder,1946;Blemetal.,1998;Codoner,1995).
There is general support or the act that birds killed
in collisions are not distinguished by age, sex, size,
or health (or example: Blem and Willis, 1998; Codo-
ner, 1995; Fink and French, 1971; Hager et al., 2008;
Klem, 1989). However, some species, such as the
White-throated Sparrow, Ovenbird, and Common
Yellowthroat, seem to be more vulnerable than oth-
ers, appearing consistently on top ten lists. Snyder(1946),examiningwindowcollisionfatalitiesatthe
Royal Ontario Museum, noted that the majority were
tunnel fyers species that requently fy through
small spaces in dense, understory habitat. Recent
work (J. A. Clark, pers. comm.) suggests that there
may be species dierences in attraction to light that
could explain these ndings. Interestingly, species
well adapted to and common in urban areas, such as
the House Sparrow and European Starling, are not
prominent on lists o atalities, and there is evidencethat resident birds are less likely to die rom collisions
than migratory birds.
Collision mortality appears to be a density-indepen-
dent phenomenon. Hager et al. (2008) compared
the number o species and individual birds killed at
buildings at Augustana College in Illinois with the
density and diversity o bird species in the surround-
ing area. The authors concluded that total window
area, habitat immediately adjacent to windows, and
APPENDIX I: THE SCIENCE OF BIRD COLLISIONS
A sample o collision victi ms rom Baltimore.Photo: Daniel J. Lebbin, ABC
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38 Bird-Friendly Building Design
behavioral dierences among species were the
best predictors o mortality patterns, rather than
simply the size and composition o the local bird
population.
From a study o multiple Manhattan buildings in
New York City, Klem et al(2009a) similarly concluded
that the expanse o glass on a building acade is the
actor most predictive o mortality rates, calculating
that every increase o 10% in the expanse o glass
correlates to a 19% increase in bird mortality in
spring, 32% in all. How well these equations predict
mortality in other cities remains to be tested. Collins
and Horn (2008) studying collisions at Millikin Uni-
versity in Illinois concluded that total glass area and
the presence/absence o large expanses o glass pre-
dicted mortality level. Hager et al(2008) came to the
same conclusion. Gelb and Delacretazs (2009) work
in New York City indicated that collisions are more
likely to occur on windows that refect vegetation.
Dr. Daniel Klem maintains running totals o the num-
ber o species reported in collision events in countries
around the world. This inormation can be ound at:
www.muhlenberg.edu/main/academics/biology/ac-
ulty/klem/aco/Country%20list.htm#World
He notes 859 species globally, with 258 rom theUnited States. The intensity o monitoring and re-
porting programs varies widely rom country to
country, however. Hager (2009) noted that window
strike mortality was reported or 45% o raptor spe-
cies ound requently in urban areas o the United
States, and represented the leading source o mor-
tality or Sharp-shinned Hawks, Coopers Hawks,
Merlins, and Peregrine Falcons.
Avian Vision and CollisionsTaking a birds-eye view is much more complicated
than it sounds. To start with, where human color vi-
sion relies on three types o sensors, birds have our,
plus an array o color lters that allow them to see
many more colors than people (Varela et al., 1993)
(see chart below). Many birds, including most pas-serines (deen and Hstad, 2003) also see into the
ultraviolet spectrum. Ultraviolet can be a compo-
nent o any color (Cuthill et al., 2000). Where humans
see red, yellow, or red + yellow, birds may see red +
yellow, but also red + ultraviolet, yellow + ultraviolet,
and red + yellow + ultraviolet, colors or which we
have no names. They can also see polarized light
(Muheim et al.,2006,2011),andtheyprocessim-
ages aster than humans; where we see continuous
motion in a movie, birds would see fickering images
(DEath, 1998; Greenwood et al., 2004; Evans et al.,
2006).Totopitallo,birdshavenotone,buttwo
receptors that permit them to sense the earths mag-
netic eld, which they use or navigation (Wiltschko et
al.,2006).
Avian Orientation andthe Earths Magnetic FieldThirty years ago, it was discovered that birds possess
the ability to orient themselves relative to the Earths
magnetic eld and locate themselves relative to
their destination. They appear to use cues rom the
sun, polarized light, stars, the Earths magnetic eld,
visual landmarks, and even odors to nd their way.
Exactly how this works and it likely varies among
nm 350 400 450 500 550 600 650
560
565
530424
445370 508
Comparison o Human and Avian Vision
Based on artwork by Sheri Williamson
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39Bird-Friendly Building Design
species is still being investigated, but there have
been interesting discoveries that also shed light on
light-related hazards to migrating birds.
Lines o magnetism between the north and south
poles have gradients in three dimensions. Cells in
birds upper beaks, or maxillae, contain the iron
compounds maghemite and magnetite. Micro-
synchrotron x-ray fuorescence analysis shows these
compounds in three dierent compartments, a
three-dimensional architecture that probably allows
birds to detect their map (Davila, 2003; Fleissner et
al., 2003, 2007). Other magnetism-detecting struc-
tures are ound in the retina o the eye, and depend
on light or activity. Light excites receptor molecules,
setting o a chain reaction. The chain in cells that re-
spond to blue wavelengths includes molecules that
react to magnetism, producing magnetic directional
cues as well as color signals. For a comprehensive
review o the mechanisms involved in avian orienta-
tion, see Wiltschko and Wiltschko, 2009.
Birds and Light Pollution
The earliest reports o mass avian mortality causedby lights were rom lighthouses, but this source o
mortality essentially disappeared when steady-burn-
ing lights were replaced by rotating beams (Jones
and Francis, 2003). Flashing or interrupted beams
apparently allow birds to continue to navigate. While
mass collision events at tall buildings and towers
havereceivedmostattention(Weir,1976;Averyet
al., 1977; Avery et al., 1978; Craword, 1981a, 1981b;
Newton, 2007), light rom many sources, rom urban
sprawl to parking lots, can aect bird behavior and
cause bird mortality (Gocheld, 1973). Gocheld (in
RichandLongcore,2006)notedthatbirdhunters
throughout the world have used lights rom res or
lanterns near the ground to disorient and net birds
on cloudy, dark nights. In a review o the eects o
articial light on migrating birds, Gauthreaux and
Belser(2006)reportontheuseofcarheadlightstoattract birds at night or tourists on saari.
Evans-Ogden (2002) showed that light emission lev-
els o sixteen buildings ranging in height rom eight
to 72 foors correlated directly with bird mortality,
and that the amount o light emitted by a structure
was a better predictor o mortality level than build-
ing height, although height was a actor. Wiltschko
et al(2007) showed that above intensity thresholds
that decrease rom green to UV, birds showed dis-
orientation. Disorientation occurs at light levels that
are still relatively low, equivalent to less than hal an
hour beore sunrise under clear sky. It is thus likely
that light pollution causes continual, widespread,
low-level mortality that collectively is a signicant
problem.
The mechanisms involved in both attraction to and
disorientation by light are poorly understood and
may dier or dierent light sources (see Gauthreaux
andBelser(2006)andHerbert(1970)forreviews.)
Recently, Haupt and Schillemeit described the paths
o 213 birds fying through beams uplighting rom
several dierent outdoor lighting schemes. Only
7.5% showed no change in behavior. Migrating birds
are severely impacted, while resident species may
show little or no eect. It is not known whether this
is because o dierences in physiology or simply a-
miliarity with local habitat.
Steady-burning red and white lights are most dangerous to birds. Photo: Mike Parr, ABC
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40 Bird-Friendly Building Design
Light Color and Avian OrientationStarting in the 1940s, ceilometers, powerul beams
o light used to measure the height o cloud cover,
came into use, and were associated with signicant
bird kills. Filtering out long (red) wavelengths and
using the blue/ultraviolet range greatly reduced
mortality. Later, replacement o xed beam ceilom-eters with rotating beams essentially eliminated
impactonmigratingbirds(Laskey,1960).Acomplex
series o laboratory studies in the 1990s demon-
strated that birds required light in order to sense the
Earths magnetic eld. Birds could orient correctly
under monochromatic blue or green light, but lon-
ger wavelengths (yellow and red) caused disorienta-
tion (Rappli et al., 2000; Wiltschko et al., 1993, 2003,
2007). It was demonstrated that the magnetic recep-
tor cells on the eyes retina are inside the type ocone cell responsible or processing blue and green
light, but disorientation seems to involve a lack o
directional inormation.
Poot et al. (2008) demonstrated that migrating birds
exposed to dierent colored lights in the eld re-
spond the same way they do in the laboratory. Birds
were strongly attracted to white and red light, and
appeared disoriented by them, especially under
overcast skies. Green light was less attractive and
minimally disorienting; blue light attracted ew birdsand did not disorient those that it did attract (but
see Evans et al., 2007). Birds were not attracted to in-
rared light. This work was the basis or development
o the Phillips Clear Sky bulb, which produces white
light with minimal red wavelengths (Marquenie et
al., 2008) and is now in use in Europe on oil rigs and
at some electrical plants. According to Van de Laar
et al. (2007), tests with this bulb on an oil platorm
during the 2007 all migration produced a 50-90%
reduction in birds circling and landing. Recently,Gehring et al. (2009) demonstrated that mortality at
communication towers was greatly reduced i strobe
lighting was used as opposed to steady-burning
white, or especially red lights. Replacement o steady-
burning warning lights with intermittent lights at
locations causing collisions is an excellent option or
protecting birds, as is manipulating light color.
Weather Impact on Collisions
Weather has a signicant and complex relationshipwith avian migration (Richardson, 1978), and large-
scale, mass mortality o migratory birds at tall, light-
ed structures (including communication towers) has
oten correlated with og or rain (Avery et al., 1977;
Craword, 1981b; Newton, 2007) The conjunction o
bad weather and lighted structures during migra-
tion is a serious threat, presumably because visual
cues used by birds or orientation are not available.
However, not all collision events take place in bad
weather. For example, in a report o mortality at a
communications tower in North Dakota (Avery et al.,
1977), the weather was overcast, usually with drizzle,
on our o the ve nights with the largest mortality.
On the th occasion, however, the weather was clear.
Landscaping and Vegetation
GelbandDelacretaz(2006,2009)evaluateddatarom collision mortality at Manhattan building a-
cades. They ound that sites where glass refected
extensive vegetation were associated with more col-
lisions than glass refecting little or no vegetation. O
the ten buildings responsible or the most collisions,
our were low-rise. Klem (2009) measured variables
in the space immediately associated with building
acades in Manhattan, as risk actors or collisions.Fog increases the danger o light both by causing birds to fy lower and byreracting light so it is visible over a larger area. Photo: Christine Sheppard, ABC
Lower foor windows are thought to be more dangerous to birds because they
are more likely to refect vegetation. Photo: Christine Sheppard, ABC
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41Bird-Friendly Building Design
Both increased height o trees and increased height
o vegetation increased the risk o collisions in all.
Ten percent increases in tree height and the height
o vegetation corresponded to 30% and 13% in-
creases in collisions in all. In spring, only tree height
had a signicant infuence, with a 10% increase
corresponding to a 22% increase in collisions. Con-
usingly, increasing acing area dened as the
distance to the nearest structure, corresponded
strongly with increased collisions in spring, and with
reduced collisions in all. Presumably, vegetation in-
creases risk both by attracting more birds to an area,
and by being refected in glass.
Research: Deterring CollisionsSystematic eorts to identiy signals that can be
used to make glass visible to birds began with the
work o Klem in 1989. Testing glass panes in the
eld and using a dichotomous choice protocol in
an aviary, Klem (1990) demonstrated that popular
devices like diving alcon silhouettes were only
eective i they were applied densely, spaced two
to our inches apart. Owl decoys, blinking holidaylights, and pictures o vertebrate eyes were among
items ound to be ineective. Grid and stripe pat-
terns made rom white material, one inch wide were
tested at dierent spacing intervals. Only three were
eective: a 3x4 inch grid, vertical stripes spaced our
inches apart, and horizontal stripes spaced about an
inch apart across the entire surace.
In urther testing using the same protocols, Klem
(2009) conrmed the eectiveness o 3MTMScotch-
calTM Perorated Window Graphic Film (also known as
CollidEscape), WindowAlert decals, i spaced at the
two- to our-inch rule, as above, and externally ap-
plied ceramic dots or rits, (0.1 inch dots spaced 0.1
inches apart). Window lms applied to the outside
surace that rendered glass opaque or translucent
were also eective. The most eective deterrents in
this study were stripes o highly refective 40% UV
lm (D. Klem, pers. comm., March 2011) alternating
This security grille also creates a pattern that will deter birds rom fying torefections. Photo: Christine Sheppard, ABC
A dense internal rit pattern on the glass o the Bike and Roll building, nearUnion Station in Washington D.C., makes it look almost opaque. Photo:Christine Sheppard, ABC
Patterns on the outside o glass, such as that shown above, are moreeective than patterns on an inside surace. Photo: Hans Schmid
A pattern o narrow horizontal stripes has proven to be highly eective atdeterring bird collisions, while covering only about 7% o the surace o theglass. Photo: Hans Schmid
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42 Bird-Friendly Building Design
with high UV absorbing stripes. Completely covering
glass with clear or refective window lm that also
absorbed UV marginally reduced collisions.
Building on Klems ndings, Rssler developed a
testing program in Austria starting in 2004 and
continuing to the present (Rssler and Zuna-Kratky,
2004; Rssler, 2005; Rssler, et al., 2007; Rssler and
Laube, 2008; Rssler, 2009). Working at the banding
center at the Hohenau Ringelsdor Biological Sta-
tion outside Vienna, Austria made possible a large
sampling o birds or each test, in some instances
permitting comparisons o a particular pattern un-
der dierent intensities o lighting. This program has
ocused primarily on geometric patterns, evaluating
the impact o dierent spacing, orientation, and di-
mensions. Birds are placed in a tunnel, where they
can view two pieces o glass: one unmodied, (the
control) and the other with the pattern to be tested.
Birds fy down the tunnel and are scored according
to whether they try to exit through the control or
the pattern. A mist net keeps the bird rom hitting
the glass and it is then released. The project ocuses
not only on nding patterns eective or deterring
collisions, but on eective patterns that cover a
minimal part o the glass surace. To date, some pat-terns have been ound to be highly eective, while
covering only 5% o the glass.
Building on Rsslers work, ABC has collaborated
with the Wildlie Conservation Society and the Carn-
egie Museum to construct a tunnel at Carnegies
Powdermill Banding Station, primarily to test com-
mercially available materials. This project has been
supported by the Association o Zoos and Aquari-
ums Conservation Endowment Fund, the Colcom
Foundation, and New York City Audubon. Results
rom the rst season showed that making an entire
surace UV refective was not an eective way to de-
ter birds. With UV materials, contrast seems to be im-
portant. Glass ritted in patterns conorming to the
2 x 4-inch rule, however, scored well as deterrents.
Most clear glass made in the United States trans-
mitsabout96%oflightfallingperpendiculartothe
outside surace, and refects about 4%. The amount
o light refected increases at sharper angles clear
glass refects about 50% o incident light at angles
over 70 degrees. Light on the inside o the glass is
also partly refected and partly transmitted. The rela-
tive intensities o light transmitted rom the inside
and refected rom the outside suraces o glass, plus
the viewing angle determine i the glass appears
transparent or mirrors the surrounding environ-
ment. Patterns on the inside suraces o glass and
objects inside the glass may not always be visible.
These changeable optical properties support the
ABCs Chris Sheppard testing a bird in the tunnel at the CarnegieMuseums Powdermill Banding Station in southwestern Pennsylvania.Photo: Susan Elbin, 2011
The tunnel an apparatus or saely testing eectiveness o dierentmaterials and designs or deterring bird collisions. Photo: ChristineSheppard, ABC
A birds eye view o glass in the tunnel. Photo: Christine Sheppard,ABC
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43Bird-Friendly Building Design
argument that patterns applied to the outer sur ace
o glass are more eective than patterns applied to
the inner surace.
The majority o the work described here uses proto-
cols that approximate a situation with ree-standing
glass birds can see through glass to the environ-
ment on the other side, patterns tested are between
the bird and the glass and patterns are primarily
back-lit. While this is useul and relevant, it does not
adequately model most glass installed in buildings.
In that situation, light levels behind the glass are
usually substantially lower than light alling on the
outside surace. New protocols have been devel-
oped to test materials whose eectiveness depends
on the glass being primarily ront-lit. This includes
UV patterns and rit patterns on the inside suraces
o insulated glass.
A panel o ritted glass, ready or testing. Photo: Christine Sheppard, ABC
Ornilux Mikados pattern refects UV wavelengths. The spiderweb eect isonly visible rom very limited viewing angles. Photo courtesy o Arnold Glass
All-over patterns such as the one shown above are less eective atdeterring collisions. Patterns with more contrast and distinct spaces, suchas the one shown on the let, are much more eective. Photo: ChristineSheppard, ABC
This glass acade, o a modern addition to the Reitberg Museum in Zrich, Germany, wasdesigned by Grazioli and Krischanitz. It eatures a surace pattern ormed o green enameltriangles, beautiul and also bird-riendly. Photo: Hans Schmidt
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Bird collisions with buildings occur year-round, but peak during
the migration period in spring and especially in fall.
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45Bird-Friendly Building Design
Bird collisions with buildings occur year-round, but
peak during the migration period in spring and
especially in all when millions o adults and juve-
nile birds travel between breeding and wintering
grounds. Migration is a complex phenomenon, and
dierent species ace dierent levels o hazards
depending on their migration strategy, immediate
weather conditions, availability o ood, and human-
made obstacles encountered on the way.
Many species have a migratory pattern that alter-
nates fight with stopovers to replenish their en-
ergy stores. Night-fying migrants, including many
songbirds, generally take o within a ew hours osunset and land ater midnight but beore dawn
(Kerlinger, 2009). Once birds have landed, they may
remain or several days, eeding and waiting or ap-
propriate weather to continue. During that time,
they make fights around the local area, hunting or
good eeding sites. Almost anywhere they stop in
cities, suburbs or business parks they run the risk
o hitting glass. Most collision monitoring programs
involve searching near dawn or birds that have
been killed or injured during the night. Programs
that also monitor during the day, however, continue
to nd birds that have collided with windows (Gelb
and Delecretaz, 2009; Olson, pers. comm; Russell,
pers. comm; Hager, 2008). These diurnal collisions
are widespread, and represent the greatest number
o bird deaths and the greatest threat to birds.
APPENDIX II: BIRD MIGRATION
Diurnal MigrantsDaytime migrants include raptors such as the Broad-
winged Hawk and Merlin that take advantage othermal air currents to reduce the energy needed or
fight. Other diurnal migrants, including Red Knots,
Canada Geese, and Sandhill Cranes, fy in focks, and
their stopover sites are localized because o their de -
pendence on bodies o water. This means that day-
time migration routes oten ollow land orms such
as rivers and mountain ranges as well as coastlines.
Birds tend to be concentrated along these routes
or fyways. Some songbird species such as the
American Robin, Horned Lark, and Eastern Kingbirdalso migrate during the day. Diurnal migrant fight
altitudes are generally lower than those o nocturnal
migrants, putting them at greater risk o collisions
with tall buildings.
As seed dispersers, birds such as the Cedar Waxwing play an important rolein maintaining many types o habitat. Photo: Chip Miller
Larger birds, such as the Sandhill Crane, migrate in focks during the day.Photo: Alan Wilson
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47Bird-Friendly Building Design
Night-migrating songbirds, already imperiled by
habitat loss, are at double the risk, threatened both
by illuminated buildings when they fy at night (see
Appendix I) and by daytime glass collisions as they
seek ood and shelter.
Millions are thus at risk as they ascend and descend,
fying through or stopping in or near populated ar-
eas. As city buildings grow in height, they become
unseen obstacles by night and pose conusing
refections by day. Nocturnal migrants, ater land-
ing, make short, low fights near dawn, searching
or eeding areas and running a gauntlet o glass
in almost every habitat, rom cities to suburbs, and
increasingly, exurbs. When weather conditions cause
night fiers to descend into the range o lighted